We began testing of the iOS 13 beta last week on several test devices that are connected to our internal mobile device network. This network passes traffic through the Palo with SSL decryption. We are finding that iOS 13, even with our cert installed on the device via MDM, does NOT accept the decrypt cert. We are still testing, but so far we have found several applications that will not work (some give errors, some just don't do anything), Safari will not open HTTPS sites, and our MDM environment cannot send commands to the devices. In all cases, once we take the device off of the internal WiFi, eliminating SSL decrypt, everything works.
I have not yet been able to find any documentation from Apple indicating that they are enforcing certificate pinning across the OS, but it sure seems like they might be. Has anyone else encountered this yet?